Catadioptric optical system

ABSTRACT

A catadioptric optical system (10, 110) capable of forming an image of an object. The system comprises a first optical axis (Z 1 ) having a first end (12) and a second end (14), with a concave mirror (M C ) arranged at the first end. A second surface (P 2 ) orthogonal to the first optical axis is provided at the second end. A reflective surface (M) is arranged between the concave mirror and the second surface. A first imaging optical system (A) comprising a first plurality of lenses (L 1  -L 4 ) is arranged between the reflective surface and the concave mirror. A second imaging optical system (B) comprising a second plurality of lenses (L 5  -L 9 ) is arranged between the reflective surface and the second surface. The system further includes a second optical axis (Z 2 ) intersecting the first optical axis at the reflective surface and having a first surface (P 1 ) disposed along and orthogonal to the secondary optical axis. The first surface is divided into first and second regions (30 and 32) by a line of intersection Q 1 , between the first surface and a plane containing the first optical axis and the second optical axis. The object is arranged in one of the first and second regions of the first surface. The image is formed in one of first and second regions (36 and 38) of the second surface formed by a line of intersection Q 2  between the second surface and a plane containing the first optical axis and the second optical axis. Alternatively, the first and second regions of the first and second surface are formed by a line of intersection between the first and second surface and a plane orthogonal to the first optical axis that includes the second optical axis. Also, an intermediate image (C) of the object is formed in the vicinity of the reflective surface. The system also preferably satisfies a number of design conditions.

FIELD OF THE INVENTION

The present invention relates to the optical system of a reductionexposure apparatus such as a stepper used principally in the manufactureof semiconductors, and more particularly relates to an approximately1/4× catadioptric reduction optical system having submicron resolutionin the ultraviolet wavelength region.

BACKGROUND OF THE INVENTION

The circuit patterns of semiconductors have been increasinglyminiaturized in recent years, and there has been a demand for higherresolving power in exposure apparatuses that print these patterns. Tosatisfy this demand, the wavelength of the light source must be madeshorter and the NA (numerical aperture) of the optical system (i.e.,projection lens) must be made larger. Nevertheless, the types of opticalglass that can withstand practical use are limited due to the absorptionof light as the wavelength shortens. Once the wavelength falls below 180nm, the only usable glass, for practical purposes, is fluorite.

However, it is impossible to correct chromatic aberration if the opticalsystem is a refractive (i.e., dioptric) optical system with only onetype of glass. Accordingly, it is extremely difficult to build adioptric optical system having the required resolving power. Therefore,a variety of proposals have been made for a catadioptric reductionoptical system, i.e., one that combines a reflective system with arefractive system comprising optical glass that can be used at theworking wavelength.

Certain of the proposed optical systems form an intermediate image oneor more times midway in the optical system. Others form an intermediateimage just once, such at those systems disclosed in Japanese PatentApplication Kokoku No. Hei 5-25170, Japanese Patent Application KokaiNo. Sho 63-163319, Japanese Patent Application Kokai No. Hei 4-234722and U.S. Pat. No. 4,779,966.

Among the abovementioned prior art, the optical systems having just oneconcave mirror include those disclosed in Japanese Patent ApplicationKokai No. Hei 4-234722 and U.S. Pat. No. 4,779,966. These opticalsystems employ only negative lenses in the round-trip combinationoptical system which includes the concave mirror, and do not use opticalsystems having positive power. Consequently, since the light beam widensas it travels toward the concave mirror, there is a tendency for thediameter of the concave mirror to increase.

Japanese Patent Application Kokai No. Hei 4-234722 in particulardiscloses a round-trip combination optical system that is completelysymmetrical. The generation of aberrations in this system is maximallycontrolled, making the correcting aberrations in successive refractiveoptical systems easier. However, since the system is symmetric, it isdifficult to obtain sufficient working distance in the vicinity of theobject plane, thereby requiring the use of a half-prism.

The optical system disclosed in U.S. Pat. No. 4,779,966 includes firstand second imaging optical systems, and uses a mirror in the secondimaging optical system, rearward of the intermediate image. However, toensure adequate brightness, the light beam needs to widen as itapproaches the concave mirror. Thus, it is difficult to make the concavemirror compact.

There is a possibility, with certain types of optical systems employinga plurality of mirrors, that the number of lenses in the refractiveoptical system can be reduced. However, these types of systems have anumber of shortcomings. For example, a phase shift method has beenconceived recently that shifts the phase of selected portions of themask, thereby raising the resolving power while preserving the depth offocus. Further, the ratio σ between the NA of the illumination opticalsystem and the NA of the imaging optical system has been made variableto enhance the imaging performance. Although an aperture stop can beinstalled in the illumination optical system to vary σ, an effectiveinstallation location for the stop cannot be found if the catadioptricoptical system mentioned earlier is made the objective lens.

In catadioptric optical systems of the type employing a round-tripoptical system of such an arrangement on the reduction side, asufficient distance from the reflective mirror to the wafer (imageplane) cannot be obtained due to issues related to the reductionmagnification. Consequently, it is unavoidable that the brightness ofthe optical system is limited, since the number of lenses constitutingthe objective lens that can be inserted in the optical path is limited.For example, even if a high-NA optical system could be realized, asufficient working distance WD between the wafer and the most wafer-wisesurface of the projection lens could not be obtained due to the need tohave a large number of optical members in a limited optical path length.

In addition, it is necessary in such conventional catadioptric opticalsystems to fold the optical path. However, the procedure of adjustingthe optical path bending member is difficult, making a high-precisionsystem difficult to realize.

Certain twice-imaging optical systems have many excellent advantages.However, to separate the light beam incident the concave mirror and thelight beam reflected from the concave mirror, these optical systems mustemploy methods, such as using a light beam separating prism or anapertured mirror, or perform separation with a reflective mirror usingan off-axis light beam.

With any of these methods, the optical axis of the optical system mustbe bent, at a right angle for example, using a reflective surface.Although this is quite easily accomplished compared with a conventionalcatadioptric optical system, this places a heavy burden on theadjustment mechanism of the optical system compared to an optical systembased on just a conventional refractive system.

In other words, since most optical systems, including refractive opticalsystems, are constructed on a single linear optical axis, if the lens ismounted shifted or tilted with respect to this optical axis, the problemcan be corrected by rotating the lens about this linear optical axis,and examining the reflected light and the like from the lens. Such anadjustment means cannot be adopted and the adjustment method becomesproblematic if the optical axis is bent.

Furthermore, only two types of adjustments exist in an optical systemcomprising a single optical axis: tilting and shifting from the opticalaxis. However, with an optical system having a plurality of opticalaxes, six degrees of freedom arise in the three-dimensional space in alens shifted from the single optical axis that forms the reference: thepositional coordinates X, Y, Z, and the rotational angles α, β, γ aboutthe X, Y, Z axes. Also, the number of components requiring suchadjustments increases significantly. Consequently, the adjustment timeincreases, the cost increases, and there are numerous difficulties justin realizing the design performance in a precision optical system. Thequestion of how to eliminate such troublesome adjustment has been apending and critical issue in round-trip optical systems.

SUMMARY OF THE INVENTION

The present invention has the objective to provide a catadioptricoptical system wherein the adjustment of the various parts is easy eventhough it has a plurality of optical axes.

To eliminate difficult adjustment of the various optical parts, thepresent invention is constructed so that the optical system thatperforms the imaging has only one optical axis.

Accordingly, a first aspect of the invention is a catadioptric opticalsystem capable of forming an image of an object. The optical systemcomprises a first optical axis having a first end and a second end, witha concave mirror arranged at the first end, and a second surfaceorthogonal to the first optical axis at the second end. A reflectivesurface is arranged between the concave mirror and the second surface. Afirst imaging optical system comprising a first plurality of lenses isarranged between the reflective surface and the concave mirror. A secondimaging optical system comprising a second plurality of lenses isarranged between the reflective surface and the second surface. Thesystem further includes a second optical axis intersecting the firstoptical axis at the reflective surface and having a first surfacedisposed along and orthogonal to the secondary optical axis and removedfrom the reflective surface. The first surface is divided into first andsecond regions by a line of intersection between the first surface and aplane containing the first optical axis and the second optical axis. Theobject is arranged in one of the first and second regions of the firstsurface The image is formed in one of first and second regions of thesecond surface formed by dividing the second surface by a line ofintersection between the second surface and a plane containing the firstoptical axis and the second optical axis. Also, the intermediate imageof the object is formed in the vicinity of the reflective surface.

A second aspect of the invention is the catadioptric optical system asdescribed above, except that the line of intersection dividing the firstand second regions of the first and second surfaces is formed by a planeorthogonal to the first optical axis that includes the second opticalaxis.

A third aspect of the invention is the catadioptric optical system asdescribed above, satisfying the following conditions:

    0.8<|D.sub.1 /H|<3

    20<|L/H|<30

wherein H is the maximum height of the object as measured from thesecond optical axis, D₁ is the distance along the secondary optical axisfrom the first surface to the reflective surface, and L is the distancealong the principal optical axis from the concave mirror to the secondsurface.

A fourth aspect of the invention is the catadioptric optical system asdescribed above, which satisfies the following condition:

    |D.sub.2 /H|<2.5

wherein D₂ is the distance along the first optical axis toward theconcave mirror from the reflective surface to a lens surface closest tothe reflective surface.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic optical diagram of a first embodiment of theoptical system of present invention;

FIG. 2 is a diagram of the object field of the optical system of FIG. 1taken along the cross-section 2--2;

FIG. 3 is a diagram of the image field of the optical system of FIG. 1taken along the cross-section 3--3;

FIG. 4 is an optical path diagram of the optical system of WorkingExample 1 of the present invention;

FIG. 5 is an optical path diagram of the optical system of FIG. 4,wherein the reflective surface of the optical system of Working Example1 is eliminated;

FIGS. 6(I)-6(IV) are aberration plots of spherical aberration,astigmatism, distortion and lateral aberrations, respectively, forWorking Example 1;

FIG. 7 is an optical path diagram of the optical system of WorkingExample 2 of the present invention;

FIG. 8(I)-8(IV) are aberration plots of spherical aberration,astigmatism, distortion and lateral aberrations, respectively, forWorking Example 2;

FIG. 9 is an optical path diagram of the optical system of WorkingExample 3 of the present invention;

FIG. 10(I)-10(IV) are aberration plots of spherical aberration,astigmatism, distortion and lateral aberrations, respectively, forWorking Example 3.

FIG. 11 is a schematic optical diagram of a second embodiment of theoptical system of present invention;

FIG. 12 is a diagram of the object field of the optical system of FIG.11 taken along the cross-section 12--12;

FIG. 13 is a diagram of the image field of the optical system of FIG. 11taken along the cross-section 13--13;

FIG. 14 is an optical path diagram of the optical system of WorkingExample 4 of the present invention;

FIGS. 15(I)-15(IV) are aberration plots of spherical aberration,astigmatism, distortion and lateral aberrations, respectively, forWorking Example 4;

FIG. 16 is an optical path diagram of the optical system of WorkingExample 5 of the present invention;

FIG. 17(I)-17(IV) are aberration plots of spherical aberration,astigmatism, distortion and lateral aberrations, respectively, forWorking Example 5;

FIG. 18 is an optical path diagram of the optical system of WorkingExample 6 of the present invention; and

FIG. 19 (I)-19(IV) are aberration plots of spherical aberration,astigmatism, distortion and lateral aberrations, respectively, forWorking Example 6.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a twice-imaging optical system having first andsecond imaging optical systems wherein an intermediate image of a second(object) surface is formed by the first imaging optical system. Theintermediate image is then reimaged onto a first (image) surface by thesecond imaging optical system. A reflective surface is provided so thata light beam from the first imaging optical system is guided to thesecond imaging optical system. The first imaging optical system isformed so that it has a round-trip optical system comprising a concavemirror and a lens group through which both the light impinging on theconcave mirror and the reflected light therefrom passes.

Based on this twice-imaging optical system, a optical system can berealized wherein an effective installation location for the stop can beobtained, and a sufficient distance between the wafer and the last(i.e., most image-wise) lens surface of the second imaging opticalsystem, namely working distance WD, can be obtained while ensuring asufficient brightness of the optical system. This allows the diameter ofthe concave mirror to be reduced and the ratio σ between the NA of theillumination optical system and the NA of the optical system to be madevariable for imaging using so-called "phase shifting" techniques. Inaddition, the adjustment procedure of the optical path bending member iscomparatively simple, and a high-precision optical system is realized.

With reference now to FIG. 1, optical system 10 comprises a firstprincipal optical axis Z₁ with an upper end 12 and a lower end 14. Aconcave mirror M_(C) is arranged along optical axis Z₁ at upper end 12and a second surface P₂ orthogonal to optical axis Z₁ is provided atlower end 14. A plurality of lenses L₁ -L₉, discussed further below, anda reflective surface M are arranged along principal optical axis Z₁between concave mirror M_(C) and second surface P₂. In FIG. 1,reflective surface M is shown as a plane mirror, but may be a reflectivesurface formed as a prism.

Optical system 10 includes a first imaging optical system A comprisinglenses L1-L4 arranged in the optical path along axis Z₁ betweenreflective surface M and concave mirror M_(C). Optical system 10 furtherincludes a second imaging optical system B comprising lenses L5-L9arranged in the optical path along axis Z₁ between reflective surface Mand second surface P₂.

First imaging optical system A constitutes a double-pass (i.e.,round-trip) optical system, meaning light passes twice in oppositedirections through the elements therein. Reflective surface M isarranged so that it folds axis Z₁ to form a secondary optical axis Z₂having an end 16. A first surface P₁ orthogonal to secondary opticalaxis Z₂ is provided along secondary optical axis Z₂ at end 16.

With reference now to FIG. 2, Q₁ is the line of intersection of firstsurface P₁ and the plane that includes both axes Z₁ and Z₂ (i.e., thepaper plane surface of FIG. 1), and RA is the illumination region of theobject. The object may be, for example, a reticle R (see FIG. 1) havinga pattern (not shown). Line Q₁ divides surface P₁ into first and secondregions 30 and 32 with the first region being positioned beneath theplane of the paper surface of FIG. 1 and the second region beingpositioned above the plane of such paper surface. The object (reticle R)may be arranged in the second region 32 of first surface P₁.

With reference now to FIG. 3, Q₂ is the line of intersection betweensecond surface P₂ and the plane that includes both optical axes Z₁ andZ₂. Line Q₂ divides surface P₂ into first and second regions 36 and 38,with the first region being positioned beneath the plane of the papersurface of FIG. 1 and the second region being positioned above the planeof such paper surface. The image of reticle R within illumination regionRA is formed in the second region 38 of second surface P₂. A wafer W isarranged at second surface P₂ and an exposure region WA is formedthereon.

With reference again to FIG. 1, the travel direction of a light beam b1proceeding from reticle R in illumination region RA is bent byreflective surface M, thereby forming a light beam b2 which enters firstimaging optical system A and then travels toward concave mirror M_(C).Light beam b2 is then reflected by concave mirror M_(C), thereby forminglight beam a b3 which travels in the reverse direction of light beam b2along an outward path, and forms intermediate image C on the rear sideof the paper surface in the vicinity of reflective surface M. In otherwords, the diameter of light beam b3 is minimized. Light beam b3 thentravels past reflective surface M, passes through second imaging opticalsystem B as a light beam b4 and reimages intermediate image C onexposure region WA of wafer W.

The portion of the pattern of reticle R that is inside illuminationregion RA is thus transferred to exposure region WA on wafer W. On theother hand, reticle R and wafer W are synchronously scanned and moved ina lateral direction orthogonal to both optical axes Z₁ and Z₂ (i.e., thedirection orthogonal to paper surface of FIG. 1). This results in theentire region of the pattern of reticle R being transferred onto waferW.

Furthermore, in the example shown in FIG. 1, although illuminationregion RA of reticle R is arranged in the second region 32 of firstsurface P1, illumination region RA can also be arranged in the firstregion 30. In this case, exposure region WA on wafer W is formed infirst region 36 of second surface P2.

Reflective surface M is used in the present invention to separate lightbeam b2 incident concave mirror M_(C) and light beam b3 reflected fromconcave mirror M_(C). However, reflective surface M is arranged externalto imaging optical systems A and B, and the optical axis of concavemirror M_(C) and the plurality of lenses constituting imaging opticalsystems A and B is a single optical axis Z₁. Consequently, the entireoptical system can be examined at its center (optical axis Z₁) and thetilt and shift of each internal lens can be detected.

Furthermore, reflective surface M may also be arranged after theadjustment of imaging optical systems A and B. In addition, there areonly two types of adjustments for reflective surface M: position (shift)and angle (tilt) with respect to axis Z₁. Furthermore, the shift andtilt error of reflective surface M in this case is not directly relatedto imaging characteristics, and is simply either a shifting or tiltingof the image. This is extremely advantageous for ensuring high-qualityimaging performance.

In other words, if the bending of optical axes Z₁ and Z₂ is performedinside imaging optical systems A and B, the adjustment of reflectivesurface M becomes extremely difficult. However, by arranging reflectivesurface M outside of imaging optical systems A and B, the adjustmentbecomes extremely easy.

If reflective surface M is thus arranged outside of imaging opticalsystems A and B, several design conditions and characteristics arenecessary from the standpoint of aberration correction and for thearrangement of the imaging optical systems. These design conditions arediscussed below.

With continuing reference to FIG. 1, first, the portion of opticalsystem 10 from the object (reticle R) to reflective surface M preferablycontains no optical elements. Thus, the size of reflective surface M isbasically determined by distance D, from reticle R to reflective surfaceM and by the objectwise NA. If distance D₁ is long, the size ofreflective surface M inevitably increases. This is not preferred, sincethere is a risk that light beam b3 reflected by concave mirror M_(C) andwhich proceeds to second imaging optical system B will interfere withreflective surface M. In addition, if reflective surface M isconstructed as a prism, distance D₁ lengthens and reflective surface Mgets larger. This is likewise not advantageous, since the prism itselfincreases in size. Accordingly, the shorter the distance D₁, the better.

However, if distance D₁ is made too short, there is a risk that reticleR will interfere with the optical path bending member comprisingreflective surface M or some other optical system member. However, byarranging reflective surface M outside of imaging optical systems A andB, the adjustment of the entire optical system 10 becomes extremelyeasy. Accordingly, it is preferred that D₁ satisfy condition (1):

    0.8<|D.sub.1 /H|<3                       (1)

wherein H is the maximum height of illumination region RA as measuredfrom axis Z₂, namely, the radius of reticle field RF. If |D₁ /H| exceedsthe upper limit in condition (1), it is difficult to separate light beamb2 of the outward path that proceeds to concave mirror M_(C) and lightbeam b3 of the return path reflected by concave mirror M_(C).Conversely, if |D₁ /H| falls below the lower limit in condition (1),there is a risk that reticle R will interfere with the optical pathbending member or some other optical system. If higher performance isdesired, then the lower limit may preferably be set at 1 and the upperlimit preferably set at 2.5.

In addition, light beam b1 widens as it moves away from reticle R, andfurther widens after being reflected by reflective surface M until it isincident the first lens surface of first imaging optical system A.Accordingly, since the effective diameter of first imaging opticalsystem A becomes smaller, it is preferable that distance D₂ along axisZ₁ from reflective surface M satisfy design condition (2):

    |D.sub.2 /H|<2.5                         (2)

If |D₂ /H| exceeds the upper limit in condition (2), the effectivediameter of first imaging optical system A increases excessively.

In addition, since there is no optical system in the optical pathbetween the object (reticle R) and reflective surface M, the correctionof distortion becomes difficult, and the distortion must be correctedalmost entirely by second imaging optical system B.

In addition, it is preferable to make the construction of optical system10 so that intermediate image C lies in the vicinity of reflectivesurface M. In other words, it is preferable to have a construction thatfits approximately in the range from the upper end of reflective surfaceM (one end face) to the lower end (end face on opposite side thereof).This is advantageous from the standpoint of separating light beam b2 andb3. In particular, since light beam b1 widens as it moves away fromreticle R, the farther is from reticle R, the larger surface M must be.For this reason, it is preferable to form the position of intermediateimage C wherein the light beam diameter is minimized, in the vicinity ofthe end of reflective surface M closest to concave mirror M_(C).

Since twice-imaging optical systems A and B are constructed on opticalaxis Z₁ in this manner, the overall length L of optical system 10increases considerably. Consequently, a portion of first imaging opticalsystem A must be shortened so that length L decreases as much aspossible.

Thus, with continuing reference to FIG. 1 and also to optical system 40of FIG. 4, it is preferable that first imaging optical system Acomprise, in order from concave mirror M_(C), at least negative meniscuslens L₁ and positive lens L₄. Furthermore, it is preferable that firstimaging optical system have, in order from the concave mirror M_(C)side, at least negative meniscus lens L₁, a positive lens L₂, a negativelens L₃ and positive lens L₄. By adopting such arrangement, the lengthof first imaging optical system A can be decreased.

If imaging optical system A is shortened too much, aberrations cannot becompletely corrected. Therefore, it is preferable the optical system ofthe present invention satisfy design condition (3):

    20<|L/H|<30                              (3)

If |L/H| exceeds the upper limit in condition (3), the size of theentire optical system becomes too large. Conversely, if |L/H| fallsbelow the lower limit in conditional expression (3), optical performancedeteriorates.

With regard to second imaging optical system B in optical system 10 ofFIG. 1, it is preferable to arrange a positive lens L₅ first in orderfrom intermediate image C toward wafer W. In so doing, divergence oflight beam b4 can be prevented, and an increase in the diameter ofoptical system 10 can also be prevented.

With reference now also to FIG. 4 and optical system 40 (to be discussedin more detail below), it is also preferable to arrange a negative lensL₆ wafer-wise and adjacent lens L₅ for correcting distortion. Inaddition, an aperture stop AS is arranged in second imaging opticalsystem B. It is also preferable to arrange a positive lens L₇ and ameniscus lens L₈ in the vicinity of aperture stop AS to correctspherical aberration. It is also preferable to arrange a positive lensL₉, whose convex surface faces the reflective surface M side, in thevicinity of the imaging plane (i.e., first surface P₁) to achieve alarge NA.

It is also preferable to employ an aspherical surface (e.g., ASP2) tocorrect spherical aberration in the vicinity of aperture stop AS, andalso to employ an aspherical surface in the positive lens in thevicinity of intermediate image C to correct distortion.

By adopting the above construction, nearly all aberrations can becorrected simultaneously. As a result, the number of lenses isultimately significantly reduced, an extremely compact optical systemcan be obtained, and the optical system can ultimately be constructedwith a single optical axis Z₁ while using a minimum of asphericalelements.

Furthermore, in the abovementioned mode for carrying out the presentinvention, illumination region RA of reticle R is arranged on firstsurface P₁, and the image of the object is formed on second surface P₂.However, this arrangement can also be reversed so that the object isarranged on second surface P₂ and the image is formed on first surfaceP₁.

In addition, although there are some difficulties with regard tomodifying the lens and adjusting the optical axis, the entire opticalsystem 10 (FIG. 1) can be made compact by arranging a very small numberof lenses, for example a positive lens, between first surface P₁ andreflective surface M, and by making first imaging optical system Ainclude this small number of lenses.

With reference again to FIGS. 1 and 2, illumination region RA of reticleR is arranged in region 32 that is on the front side of the papersurface of first surface P₁. Also, with reference again to FIG. 3,exposure region WA of wafer W is arranged in region 38. As a result, thescanning direction of reticle R and wafer W is the lateral directionorthogonal to both optical axes Z₁ and Z₂ (i.e., the directionorthogonal to the paper surface of FIG. 1).

In place of this construction, illumination region RA of reticle R canalso be arranged in region 30 and exposure region WA of wafer W can bearranged in region 38. With this construction, the scanning direction ofreticle R is the longitudinal direction parallel to principal opticalaxis Z₁, and the scanning direction of wafer W is the direction parallelto secondary optical axis Z₂.

With this longitudinal scan-type construction, reflective surface M islong in the left-right direction, and short in the depth direction whenviewed from the side of reticle R arranged on first surface P1 (e.g.,the view of FIG. 1). On the other hand, since the diameter of light beamb1 increases in the depth direction, reflective surface M can be madesmaller by reflecting the light beam on the lower end of reflectivesurface M, which is a shorter distance from reticle R.

However, with the lateral scan-type construction according to thepresent invention, reflective surface M is short in the left-rightdirection and long in the depth direction when viewed from the side ofreticle R. Further, the diameter of light beam b1 increases in the depthdirection. Accordingly, there is a disadvantage in that the size ofreflective surface M ultimately increases.

According to the longitudinal scan-type construction, the scanningdirection of reticle R arranged on the first surface is the directionparallel to the optical axis Z₁, and the scanning direction of wafer Wis the direction parallel to optical axis Z₂. Further, principal opticalaxis Z₁ is generally arranged in the vertical direction, the scanningdirection of reticle R is the vertical direction.

Accurate scanning in the horizontal direction can be realized withcomparative ease. However, if scanning is in the vertical direction,gravity continuously acts in the scanning direction and a force oppositeto gravity must be added to compensate. Accordingly, accurate scanninggenerally cannot be easily realized.

To solve this problem, it is preferable to make the scanning directionof reticle R and the scanning direction of wafer W both horizontal.However, in this case, optical axis Z₁ is in the horizontal directionand, accordingly, all lenses comprising the optical system are arrangedvertically. Thus, there is a risk that the lenses themselves will deformas well as a risk the lenses will slip due to gravity when handlingduring adjustment.

In contrast, in the present invention, both the scanning direction ofreticle R and the scanning direction of wafer W are orthogonal to bothoptical axes Z₁ and Z₂. Therefore, principal optical axis Z₁ can bealigned with the vertical direction. Also, the scanning direction ofreticle R and the scanning direction of wafer W can be made thehorizontal direction. This allows for scanning to be performed withoutthe need to compensate for gravity.

WORKING EXAMPLES

The following describes Working Examples 1-6 of the present invention.Each of the Working Examples apply the optical system according to thepresent invention to a scanning-type exposure apparatus.

Tables 1-6 below list the various specifications of Working Example 1 toWorking Example 6, respectively. In the "Principal Specifications"section in Tables 1A-6A, λ is the working wavelength, β is theprojection magnification, NA is the imagewise numerical aperture, and .Oslashed._(max) is the maximum effective diameter of the lens. In the"Specifications of Optical Members" section of these tables, S in thefirst column is the number of each optical surface from the reticle Rside, r in the second column is the radius of curvature of each opticalsurface, d in the third column is the axial spacing from each opticalsurface to the next optical surface. In Tables 1A-3A, the fourth columnG is the glass type. Also included as the last column in Tables 1A-6A isa column E representing the symbol for each optical surface or opticalelement.

The refractive index n of the fused quartz (SiO₂) and fluorite (CaF₂) atthe working wavelength (λ=193 nm) is as follows.

SiO₂ : n=1.56033

CaF₂ : n=1.50146

In addition, optical surfaces with an asterisk (*) in first column Sindicates an aspherical surface, and the value of r in the second columnfor aspherical surfaces indicates the vertex radius of curvature.

The shape of an aspherical surface is described by:

    z(y)=(y.sup.2 /r)/{1+(1-(1+κ)y.sup.2 /r.sup.2).sup.1/2 }+Ay.sup.4 +By.sup.6 +Cy.sup.8 +Dy.sup.10

wherein,

y=height from the optical axis,

z=distance in the optical axis direction from the tangential plane tothe aspherical surface,

r=vertex radius of curvature,

κ=conical coefficient, and

A, B, C, D=aspherical coefficients.

Further, the aspherical coefficients A, B, C, D are shown in Tables1B-6B Aspherical Surface Data. The conical coefficient κ is 0.0 for eachaspherical surface.

Exposure region WA of the optical system in each Working Example is arectangular aperture measuring 25×6.6 mm. However, by scanning wafer Wrelative to exposure region WA, the entire exposure surface area onwafer W, for example a region measuring 25×33 mm, can be exposed.

In addition, in Working Examples 1-3, the effective diameter of theworking lenses is approximately the same as or less than refractivespherical optical systems normally used for this specification. ForWorking Examples 3-6, the effective diameter of the working lenses isapproximately 3/4 that of refractive spherical optical systems normallyused for this specification. Also, for Working Examples 1-6, the numberof working lenses is also small at approximately half that of refractivespherical optical systems.

In each aberration plot (FIGS. 6, 8, 10, 15, 17 and 19), NA indicatesthe imagewise numerical aperture, and Y indicates the image height. Inaddition, in each astigmatism plot (FIGS. 6(II), 8(II), 10(II), 15(II),17(II) and 18(II)), dotted line M indicates the meridional image plane,and solid line S indicates the sagittal image plane.

WORKING EXAMPLES 1-3

Working Examples 1-3 are representative of a first embodiment of theoptical system of the present invention. Optical systems 40 and 50(FIGS. 4 and 5, respectively) represent variations of Working Example 1.In these optical systems, light beam separating mirror M is arrangedafter reticle R.

With reference now to FIG. 4 and optical system 40 of Working Example 1,first imaging optical system A is a round-trip optical systemcomprising, in order along optical axis Z₁ from the mirror M side, twopositive lenses A₁ and A₂, a negative lens A₃, a negative meniscus lensA₄, a positive lens A₅, a negative lens A₆, a positive lens A₇, anegative lens A₈, a positive lens A₉, a negative meniscus lens A₁₀,whose concave surface faces the mirror M side, and concave mirror M_(C).

Second imaging optical system B comprises, in order along optical axisZ₁ from the mirror M side toward wafer W, a positive lens B₁, a negativemeniscus lens B₂, a positive lens B₃, a negative lens B₄, a positivelens B₅, aperture stop AS, a meniscus lens B₆, three positive lenses B₇,B₈ and B₉, a negative lens B₁₀ and a positive lens B₁₁ whose convexsurface faces the light beam separating mirror M side. The glassmaterial of all lenses is fused quartz.

                  TABLE 1A                                                        ______________________________________                                        DESIGN SPECIFICATION                                                          ______________________________________                                        Principal Specifications:                                                                       = 193 nm (ArF Excimer Laser)                                β = 1/4     NA = 0.75                                                    H = 69.76 mm     D.sub.1 = 136.1 mm                                                                        D.sub.2 = 121.6 mm                               L = 1981 mm      .o slashed..sub.max = 275 mm                                 Exposure Field: 25 × 6.6 mm                                             |D.sub.1 /H| = 1.95                                                          |D.sub.2 /H| = 1.74                                                     |L/H| = 28.4                   S      r          d           G     E                                         ______________________________________                                         0     ∞    136.100000        R                                          1     ∞    -121.622282       M                                          2     -1967.58802                                                                              -36.300000  SiO.sub.2                                                                           A.sub.1                                                                             L.sub.4                              3     461.23833  -0.106920                                                    4     -264.03622 -44.000000  SiO.sub.2                                                                           A.sub.2                                                                             L.sub.4                              5     -1512.13989                                                                              -131.494209                                                  6     1221.82968 -29.700000  SiO.sub.2                                                                           A.sub.3                                    7     -25338.03804                                                                             -0.299345                                                    8     -664.00557 -27.500000  SiO.sub.2                                                                           A.sub.4                                    9     -148.84974 -24.814835                                                  10     -251.86051 -49.500000  SiO.sub.2                                                                           A.sub.5                                   11     360.39841  -0.100000                                                   12     482.78552  -18.700000  SiO.sub.2                                                                           A.sub.6                                   13     -281.19596 -5.034093                                                   14     -563.37964 -27.500000  SiO.sub.2                                                                           A.sub.7                                   15     -2045.99337                                                                              -20.460000                                                  16     235.10356  -18.700000  SiO.sub.2                                                                           A.sub.8                                   17     -4300.32289                                                                              -1.594260                                                   18     -426.84111 -27.500000  SiO.sub.2                                                                           A.sub.9                                   19     4351.96037 -13.911919                                                  20     209.48701  -19.800000  SiO.sub.2                                                                           A.sub.10                                                                            L.sub.1                             21     296.68194  -31.698975                                                  22     328.68841  31.698975         M.sub.C                                   23     296.68194  19.800000   SiO.sub.2                                                                           A.sub.10                                  24     209.48701  13.911919                                                   25     4351.96037 27.500000   SiO.sub.2                                                                           A.sub.9                                   26     -426.84111 1.594260                                                    27     -4300.32289                                                                              18.700000   SiO.sub.2                                                                           A.sub.8                                   28     235.10356  20.460000                                                   29     -2045.99337                                                                              27.500000   SiO.sub.2                                                                           A.sub.7                                   30     -563.37964 5.034093                                                    31     -281.19596 18.700000   SiO.sub.2                                                                           A.sub.6                                   32     482.78552  0.100000                                                    33     360.39841  49.500000   SiO.sub.2                                                                           A.sub.5                                   34     -251.86051 24.814835                                                   35     -148.84974 27.500000   SiO.sub.2                                                                           A.sub.4                                   36     -664.00557 0.299345                                                    37     -25338.03804                                                                             29.700000   SiO.sub.2                                                                           A.sub.3                                   38     1221.82968 131.494209                                                  39     -1512.13989                                                                              44.000000   SiO.sub.2                                                                           A.sub.2                                   40     -264.03622 0.106920                                                    41     461.23833  36.300000   SiO.sub.2                                                                           A.sub.1                                   42     -1967.58802                                                                              414.335315                                                  *43    6876.44925 44.000000   SiO.sub.2                                                                           B.sub.1                                                                             L.sub.5                             44     -488.24425 98.273364                                                   45     949.54747  23.100000   SiO.sub.2                                                                           B.sub.2                                                                             L.sub.6                             46     380.00000  10.438319                                                   47     824.60830  49.500000   SiO.sub.2                                                                           B.sub.3                                   48     -11352.29016                                                                             254.550884                                                  49     -51712.00506                                                                             26.400000   SiO.sub.2                                                                           B.sub.4                                   50     310.24257  6.440918                                                    51     378.70003  61.600000   SiO.sub.2                                                                           B.sub.5                                                                             L.sub.7                             52     -835.09235 86.082771                                                   53     --         37.011572         AS                                        54     312.99786  27.500000   SiO.sub.2                                                                           B.sub.6                                                                             L.sub.8                             *55    317.35784  4.761030                                                    56     265.14846  49.500000   SiO.sub.2                                                                           B.sub.7                                   57     -2270.69764                                                                              15.548079                                                   58     231.99665  60.500000   SiO.sub.2                                                                           B.sub.8                                   59     -14822.69804                                                                             67.603735                                                   60     143.66448  36.300000   SiO.sub.2                                                                           B.sub.9                                   61     827.06470  10.206244                                                   62     -5784.09653                                                                              13.200000   SiO.sub.2                                                                           B.sub.10                                  63     404.40593  0.100000                                                    64     185.03629  49.500000   SiO.sub.2                                                                           B.sub.11                                                                            L.sub.9                             65     2867.73663 6.000000                                                    66     ∞                      W                                         ______________________________________                                    

                  TABLE 1B                                                        ______________________________________                                        ASPHERICAL SURFACE DATA                                                       ______________________________________                                        S43  A =     -0.446592 × 10.sup.-8                                                                 B =   -0.453957 × 10.sup.-14                      C =     -0.205385 × 10.sup.-18                                                                D =   -0.485866 × 10.sup.-23                 S55  A =       0.130299 × 10.sup.-7                                                                B =     0.108307 × 10.sup.-12                     C =       0.107069 × 10.sup.-17                                                               D =     0.132127 × 10.sup.-22                ______________________________________                                    

With reference now to FIG. 7 and optical system 70 of Working Example 2,light beam separating mirror M is arranged after reticle R.

First imaging optical system A of optical system 70 is a round-tripoptical system comprising, in order along optical axis Z₁ from themirror M side, two positive lenses A₁ and A₂, a meniscus lens A₃, anegative meniscus lens A₄, a positive lens A₅, a negative lens A₆, apositive lens A₇, a negative lens A₈, a positive lens A₉, a negativemeniscus lens A₁₀ whose concave surface faces the mirror M side, andconcave mirror M_(C).

Second imaging optical system B comprises, in order from the mirror Mside, positive lens B₁, a negative lens B₂, a positive lens B₃, anegative lens B₄, a positive lens B₅, aperture stop AS, a meniscus lensB₆, three positive lenses B₇, B₈, and B₉, a negative lens B₁₀ and apositive lens B₁₁ whose convex surface faces the mirror M side. Theglass material of lenses A₉ and B₄ is fluorite, and the glass materialof the other lenses is fused quartz.

                  TABLE 2A                                                        ______________________________________                                        DESIGN SPECIFICATION                                                          ______________________________________                                        Principal Specifications:                                                                       = 193 nm (ArF Excimer Laser)                                β = 1/4     NA = 0.75                                                    H = 68.2 mm      D.sub.1 = 145.1 mm                                                                        D.sub.2 = 112.6 mm                               L = 1944 mm      .o slashed..sub.max = 259 mm                                 Exposure Field: 25 × 6.6 mm                                             |D.sub.1 /H| = 2.13                                                          |D.sub.2 /H| = 1.65                                                     |L/H| = 28.5                   S      r          d           G     E                                         ______________________________________                                         0     ∞    145.100000        R                                          1     ∞    -112.591130       M                                          2     -1967.58802                                                                              -36.300000  SiO.sub.2                                                                           A.sub.1                                                                             L.sub.4                              3     461.23833  -0.106920                                                    4     -321.33912 -44.000000  SiO.sub.2                                                                           A.sub.2                                                                             L.sub.4                              5     -2100.88923                                                                              -122.583142                                                  6     501.10504  -29.700000  SiO.sub.2                                                                           A.sub.3                                    7     541.11926  -0.324595                                                    8     -473.18044 -27.500000  SiO.sub.2                                                                           A.sub.4                                    9     -196.17212 -62.580381                                                  10     -3779.07966                                                                              -30.000000  SiO.sub.2                                                                           A.sub.5                                   11     387.11621  -4.367656                                                   12     412.88313  -18.700000  SiO.sub.2                                                                           A.sub.6                                   13     -192.61791 -1.582265                                                   14     -201.03547 -35.000000  SiO.sub.2                                                                           A.sub.7                                   15     -1414.97510                                                                              -20.460000                                                  16     204.63720  -18.700000  SiO.sub.2                                                                           A.sub.8                                   17     100789.97971                                                                             -0.100000                                                   18     -695.29793 -40.000000  CaF.sub.2                                                                           A.sub.9                                   19     292.92171  -95.224100                                                  20     209.38224  -19.800000  SiO.sub.2                                                                           A.sub.10                                                                            L.sub.1                             21     533.83495  -15.723944                                                  22     333.25466  15.723944         M.sub.C                                   23     533.83495  19.800000   SiO.sub.2                                                                           A.sub.10                                  24     209.38224  95.224100                                                   25     292.92171  40.000000   CaF.sub.2                                                                           A.sub.9                                   26     -695.29793 0.100000                                                    27     100789.97971                                                                             18.700000   SiO.sub.2                                                                           A.sub.8                                   28     204.63720  20.460000                                                   29     -1414.97510                                                                              35.000000   SiO.sub.2                                                                           A.sub.7                                   30     -201.03547 1.582265                                                    31     -192.61791 18.700000   SiO.sub.2                                                                           A.sub.6                                   32     412.88313  4.367656                                                    33     387.11621  30.000000   SiO.sub.2                                                                           A.sub.5                                   34     -3779.07966                                                                              62.580381                                                   35     -196.17212 27.500000   SiO.sub.2                                                                           A.sub.4                                   36     -473.18044 0.324595                                                    37     541.11926  29.700000   SiO.sub.2                                                                           A.sub.3                                   38     501.10504  122.583142                                                  39     -2100.88923                                                                              44.000000   SiO.sub.2                                                                           A.sub.2                                   40     -321.33912 0.106920                                                    41     461.23833  36.300000   SiO.sub.2                                                                           A.sub.1                                   42     -1967.58802                                                                              442.591130                                                  *43    1891.18025 40.000000   SiO.sub.2                                                                           B.sub.1                                                                             L.sub.5                             44     -646.79536 91.872138                                                   45     723.36962  21.000000   SiO.sub.2                                                                           B.sub.2                                                                             L.sub.6                             46     309.77480  11.273401                                                   47     614.63478  45.000000   SiO.sub.2                                                                           B.sub.3                                   48     -4366.41782                                                                              199.362566                                                  49     -1798.05238                                                                              24.000000   CaF.sub.2                                                                           B.sub.4                                   50     275.00000  2.000000                                                    51     290.42916  60.000000   SiO.sub.2                                                                           B.sub.5                                                                             L.sub.7                             52     -483.42767 38.284844                                                   53     --         30.904398         AS                                        54     338.19712  25.100000   SiO.sub.2                                                                           B.sub.6                                                                             L.sub.8                             *55    276.01919  1.423682                                                    56     240.27695  55.000000   SiO.sub.2                                                                           B.sub.7                                   57     -626.12954 4.097833                                                    58     181.45355  52.000000   SiO.sub.2                                                                           B.sub.8                                   59     322.99376  50.392410                                                   60     150.71383  33.000000   SiO.sub.2                                                                           B.sub.9                                   61     -1959.54185                                                                              1.388394                                                    62     -981.40546 12.000000   SiO.sub.2                                                                           B.sub.10                                  63     956.38699  0.378132                                                    64     211.73541  74.737842   SiO.sub.2                                                                           B.sub.11                                                                            L.sub.9                             65     2253.26069 6.000000                                                    66     ∞                      W                                         ______________________________________                                    

                  TABLE 2B                                                        ______________________________________                                        ASPHERICAL SURFACE DATA                                                       ______________________________________                                        S43  A =     -0.540229 × 10.sup.-8                                                                 B =     0.302102 × 10.sup.-14                     C =       0.214457 × 10.sup.-20                                                               D =     0.311899 × 10.sup.-23                S55  A =       0.119727 × 10.sup.-7                                                                B =     0.127533 × 10.sup.-12                     C =       0.785499 × 10.sup.-18                                                               D =   -0.270797 × 10.sup.-23                 ______________________________________                                    

With reference now to FIG. 9 and optical system 90 of Working Example 3,light beam separating mirror M is arranged after reticle R.

First imaging optical system A of projector optical system 90 is around-trip optical system comprising, in order along optical axis Z₁from the mirror M side, two positive lenses A₁ and A₂, a meniscus lensA₃, a negative meniscus lens A₄, a positive lens A₅, a negative lens A₆,a positive lens A₇, a negative lens A₈, a positive lens A₉, a negativemeniscus lens A₁₀ whose concave surface faces the mirror M side, andconcave mirror M_(C).

Second imaging optical system B comprises, in order from the mirror Mside, a positive lens B₁, a negative lens B₂, a positive lens B₃, anegative lens B₄, a positive lens B₅, aperture stop AS, a meniscus lensB₆, three positive lenses B₇, B₈ and B₉, a negative lens B₁₀, and apositive lens B₁₁ whose convex surface faces the light beam separatingmirror M side. The glass material of all the lenses is fused quartz.

                  TABLE 3A                                                        ______________________________________                                        DESIGN SPECIFICATION                                                          ______________________________________                                        Principal Specifications:                                                                       = 193 nm (ArF Excimer Laser)                                β = 1/4     NA = 0.77                                                    H = 66.8 mm      D.sub.1 = 125.1 mm                                                                        D.sub.2 = 110.0 mm                               L = 1734 mm      .o slashed..sub.max = 251 mm                                 Exposure Field: 25 × 6.6 mm                                             |D.sub.1 /H| = 1.87                                                          |D.sub.2 /H| = 1.65                                                     |L/H| = 26.0                   S      r          d           G     E                                         ______________________________________                                         0     ∞    125.100000        R                                          1     ∞    -110.000000       M                                          2     -1788.71693                                                                              -33.000000  SiO.sub.2                                                                           A.sub.1                                                                             L.sub.4                              3     419.30758  -0.097200                                                    4     -250.51272 -40.000000  SiO.sub.2                                                                           A.sub.2                                                                             L.sub.4                              5     -2095.38285                                                                              -132.582944                                                  6     280.08897  -27.000000  SiO.sub.2                                                                           A.sub.3                                    7     286.06919  -0.100000                                                    8     -2344.69801                                                                              -25.000000  SiO.sub.2                                                                           A.sub.4                                    9     -139.16277 -10.583805                                                  10     -230.81019 -45.000000  SiO.sub.2                                                                           A.sub.5                                   11     289.72574  -0.100000                                                   12     396.50913  -17.000000  SiO.sub.2                                                                           A.sub.6                                   13     -202.10491 -2.545072                                                   14     -245.66623 -25.000000  SiO.sub.2                                                                           A.sub.7                                   15     -850.43638 -18.600000                                                  16     191.90096  -17.000000  SiO.sub.2                                                                           A.sub.8                                   17     1441.97113 -8.542734                                                   18     -319.52135 -25.000000  SiO.sub.2                                                                           A.sub.9                                   19     -1032.91485                                                                              -35.037850                                                  20     229.55442  -18.000000  SiO.sub.2                                                                           A.sub.10                                                                            L.sub.1                             21     391.22655  -20.529633                                                  22     293.81625  20.529633         M.sub.C                                   23     391.22655  18.000000   SiO.sub.2                                                                           A.sub.10                                  24     229.55442  35.037850                                                   25     -1032.91485                                                                              25.000000   SiO.sub.2                                                                           A.sub.9                                   26     -319.52135 8.542734                                                    27     1441.97113 17.000000   SiO.sub.2                                                                           A.sub.8                                   28     191.90096  18.600000                                                   29     -850.43638 25.000000   SiO.sub.2                                                                           A.sub.7                                   30     -245.66623 2.545072                                                    31     -202.10491 17.000000   Si0.sub.2                                                                           A.sub.6                                   32     396.50913  0.100000                                                    33     289.72574  45.000000   SiO.sub.2                                                                           A.sub.5                                   34     -230.81019 10.583805                                                   35     -139.16277 25.000000   SiO.sub.2                                                                           A.sub.4                                   36     -2344.69801                                                                              0.100000                                                    37     286.06919  27.000000   SiO.sub.2                                                                           A.sub.3                                   38     280.08897  132.582944                                                  39     -2095.38285                                                                              40.000000   SiO.sub.2                                                                           A.sub.2                                   40     -250.51272 0.097200                                                    41     419.30758  33.000000   SiO.sub.2                                                                           A.sub.1                                   42     -1788.71639                                                                              347.180778                                                  *43    1555.13047 40.000000   SiO.sub.2                                                                           B.sub.1                                                                             L.sub.5                             44     -360.06064 118.910547                                                  45     -397.98234 21.000000   SiO.sub.2                                                                           B.sub.2                                                                             L.sub.6                             46     301.16710  6.265312                                                    47     456.49362  45.000000   SiO.sub.2                                                                           B.sub.3                                   48     -457.50529 216.938305                                                  49     -912.13011 24.000000   SiO.sub.2                                                                           B.sub.4                                   50     285.72541  2.779460                                                    51     324.54787  56.000000   SiO.sub.2                                                                           B.sub.5                                                                             L.sub.7                             52     -517.93077 33.030511                                                   53     --         10.000000         AS                                        54     232.91811  25.000000   SiO.sub.2                                                                           B.sub.6                                                                             L.sub.8                             *55    247.47594  13.513156                                                   56     272.86464  45.000000   SiO.sub.2                                                                           B.sub.7                                   57     -1299.32741                                                                              13.009095                                                   58     181.50497  55.000000   SiO.sub.2                                                                           B.sub.8                                   59     3103.88212 57.514255                                                   60     122.59580  33.000000   SiO.sub.2                                                                           B.sub.9                                   61     842.87047  6.906830                                                    62     2024.08428 12.000000   SiO.sub.2                                                                           B.sub.10                                  63     171.55062  0.100000                                                    64     121.12960  45.000000   SiO.sub.2                                                                           B.sub.11                                                                            L.sub.9                             65     1872.51465 6.000000                                                    66     ∞                      W                                         ______________________________________                                    

                  TABLE 3B                                                        ______________________________________                                        ASPHERICAL SURFACE DATA                                                       ______________________________________                                        S43  A =     -0.564743 × 10.sup.-8                                                                 B =     0.301731 × 10.sup.-14                     C =     -0.487516 × 10.sup.-18                                                                D =   -0.257273 × 10.sup.-22                 S55  A =       0.191005 × 10.sup.-7                                                                B =     0.183987 × 10.sup.-12                     C =       0.211392 × 10.sup.-17                                                               D =     0.297490 × 10.sup.-22                ______________________________________                                    

It can be clearly seen from the aberration plots in FIGS. 6, 8 and 10corresponding respectively to Working Examples 1-3, in the unitwavelength of 193 nm in Working Example 1 and Working Example 3, and inthe wavelength range of 193 nm ±5 pm in Working Example 2, excellentimaging performance is obtained and aberrations are corrected to nearlyan aberration-free state for each Working Example.

WORKING EXAMPLES 3-6

Optical system 110 of FIG. 11 is similar to optical system 10 of FIG. 1,and represents a second embodiment of the present invention. In opticalsystem 110, reflecting surface (i.e., light beam separating mirror) M issmaller than in Working Examples 1-3. Also, in optical system 110 andWorking Examples 4-6 based thereon, the effective diameter of theoptical system is small, at approximately 3/4 that of refractivespherical optical systems normally used at the present specifications.In addition, the number of lenses is also small, being about half thatof refractive spherical optical systems with similar specifications.Also, the lines of intersection Q₁ and Q₂ dividing the first and secondregions 112,114 and 120,122 of first and second surfaces P₁ and P₂respectively, are formed by a plane orthogonal to first optical axis Z₁that includes second optical axis Z₂.

With reference now to FIG. 14 and optical system 140 of Working Example4, light beam separating mirror M is arranged after reticle R. Inaddition, first imaging optical system A comprises a round-trip opticalsystem wherein, in order from the light beam separating mirror M side,two positive lenses A1 and A2, a meniscus lens A3, a negative meniscuslens A4, a positive lens A5, a negative lens A6, a positive lens A7, anegative meniscus lens A8 whose concave surface faces the light beamseparating mirror M side, and concave mirror M_(C).

Second imaging optical system B comprises, in order from the mirror Mside, positive lens B1, negative lens B2, positive lens B3, negativelens B4, positive lens B5, aperture stop AS, meniscus lens B6, threepositive lenses B7, B8 and B9, negative lens B10, and positive lens B11whose convex surface faces the mirror M side.

                  TABLE 4A                                                        ______________________________________                                        SPECIFICATION OF OPTICAL MEMBERS                                              ______________________________________                                        Principal Specifications:                                                                       = 193 nm (ArF Excimer Laser)                                β = 1/4     NA = 0.7                                                     H = 70.36 mm     D = 160.1 mm                                                                              D.sub.2 = 10.0 mm                                L = 1534 mm      .o slashed..sub.max = 220 mm                                 Exposure Field: 25 × 6.6 mm                                             |D.sub.1 /H| = 2.28                                                          |D.sub.2 /H| = 0.14                                                     |L/H| = 21.8                   S       r          d             E                                            ______________________________________                                         0      ∞    160.100000    R                                             1      ∞    -10.000000    M                                             2      -1788.71639                                                                              -29.000000    A.sub.1                                                                             L.sub.4                                 3      419.30758  -0.097200                                                   4      -250.61403 -33.000000    A.sub.2                                                                             L.sub.4                                 5      -6136.00339                                                                              -138.422781                                                 6      244.13129  -27.000000    A.sub.3                                       7      236.86664  -0.200000                                                   8      -441.03076 -17.000000    A.sub.4                                       9      -130.33902 -13.232045                                                 10      -391.22278 -19.000000    A.sub.5                                      11      -4917.23961                                                                              -18.600000                                                 12      245.26287  -17.000000    A.sub.6                                                                             L.sub.3                                13      -1615.89591                                                                              -1.843450                                                  14      -241.95870 -25.000000    A.sub.7                                                                             L.sub.2                                15      14452.00549                                                                              -62.163582                                                 16      145.04293  -18.000000    A.sub.8                                                                             L.sub.1                                17      347.29355  -19.661891                                                 18      248.23614  19.661891     M.sub.C                                      19      347.29355  18.000000     A.sub.8                                      20      145.04293  62.163582                                                  21      14452.00549                                                                              25.000000     A.sub.7                                      22      -241.95870 1.843450                                                   23      -1615.89591                                                                              17.000000     A.sub.6                                      24      245.26287  18.600000                                                  25      -4917.23957                                                                              19.000000     A.sub.5                                      26      -391.22278 13.232045                                                  27      -130.33902 17.000000     A.sub.4                                      28      -441.03076 0.200000                                                   29      236.86664  27.000000     A.sub.3                                      30      244.13129  138.422781                                                 31      -6136.00339                                                                              33.000000     A.sub.2                                      32      -250.61403 0.097200                                                   33      419.30758  29.000000     A.sub.1                                      34      -1788.71639                                                                              291.668555                                                 *35     8637.19547 32.000000     B.sub.1                                                                             L.sub.5                                36      -278.32248 120.501173                                                 37      -284.21267 21.000000     B.sub.2                                                                             L.sub.6                                38      380.00000  7.640330                                                   39      977.55302  45.000000     B.sub.3                                      40      -289.72006 188.674290                                                 41      -782.07989 24.000000     B.sub.4                                      42      275.00000  2.199165                                                   43      311.81819  56.000000     A.sub.5                                                                             L.sub.7                                44      -375.13741 11.588720                                                  45      --         10.000000     AS                                           46      196.65458  25.000000     B.sub.6                                                                             L.sub.8                                *47     180.51391  10.087193                                                  48      253.87648  40.000000     B.sub.7                                      49      8600.70931 2.214198                                                   50      157.11074  48.000000     B.sub.8                                      51      1256.41165 55.106219                                                  52      113.93043  33.0000000    B.sub.9                                      53      886.99217  8.485632                                                   54      -18818.69933                                                                             12.000000     B.sub.10                                     55      207.40711  0.100000                                                   56      109.31199  45.000000     B.sub.11                                                                            L.sub.9                                57      14193.19706                                                                              6.000000                                                   58      ∞                  W                                            ______________________________________                                    

                  TABLE 4B                                                        ______________________________________                                        ASPHERICAL SURFACE DATA                                                       ______________________________________                                        S35  A =     -0.123690 × 10.sup.-7                                                                 B =     0.129803 × 10.sup.-13                     C =     -0.212874 × 10.sup.-18                                                                D =   -0.943396 × 10.sup.-22                 S47  A =       0.136582 × 10.sup.-7                                                                B =     0.193143 × 10.sup.-12                     C =       0.306903 × 10.sup.-17                                                               D =     0.487055 × 10.sup.-22                ______________________________________                                    

With reference now to FIG. 16 and optical system 160 of Working Example5, a light beam separating prism P is arranged after reticle R. Inaddition, first imaging optical system A comprises a round-trip opticalsystem wherein, in order from the light beam separating prism P side,two positive lenses A1 and A2, a meniscus lens A3, a negative meniscuslens A4, a positive lens A5, a negative lens A6, a positive lens A7, anegative meniscus lens A8 whose concave surface faces the light beamseparating prism P side, and concave mirror M_(C).

Second imaging optical system B comprises, in order from the light beamseparating prism P side, a positive lens B1, a negative lens B2, apositive lens B3, a negative lens B4, a positive lens B5, aperture stopAS, a meniscus lens B6, three positive lenses B7, B8 and B9, a negativelens B10, and a positive lens B11 whose convex surface faces the lightbeam separating prism P side.

                  TABLE 5A                                                        ______________________________________                                        DESIGN SPECIFICATION                                                          ______________________________________                                        Principal Specifications:                                                                       = 193 nm (ArF Excimer Laser)                                β = 1/4     NA = 0.75                                                    H = 70.36 mm     D = 190.1 mm                                                                              D.sub.2 = 20.0 mm                                L = 1693 mm      .o slashed..sub.max = 234 mm                                 Exposure Field: 25 × 6.6 mm                                             |D/H| = 2.70                                                                 |D.sub.2 /H| = 0.28                                                     |L/H| = 24.1                   S       r          d             E                                            ______________________________________                                         0      ∞    85.100000     R                                             1      ∞    105.000000    P                                             2      ∞    -15.000000    PM                                            3      ∞    -5.000000                                                   4      -1788.71639                                                                              -29.000000    A.sub.1                                                                             L.sub.4                                 5      419.30758  -0.097200                                                   6      -310.64095 -33.000000    A.sub.2                                                                             L.sub.4                                 7      -2807.83665                                                                              -152.548704                                                 8      287.16506  -27.000000    A.sub.3                                       9      255.48240  -0.200000                                                  10      -367.14810 -17.000000    A.sub.4                                      11      -141.19742 -14.911131                                                 12      -398.90704 -19.000000    A.sub.5                                      13      -608.94218 -18.600000                                                 14      232.39912  -17.000000    A.sub.6                                                                             L.sub.3                                15      1698.12647 -15.952383                                                 16      -327.74499 -25.000000    A.sub.7                                                                             L.sub.2                                17      6237.96729 -61.535574                                                 18      166.40938  -18.000000    A.sub.8                                                                             L.sub.1                                19      395.75289  -55.022688                                                 20      301.44131  55.022688     M.sub.C                                      21      395.75289  18.000000     A.sub.8                                      22      166.40938  61.535574                                                  23      6237.96729 25.000000     A.sub.7                                      24      -327.74499 15.952383                                                  25      1698.12647 17.000000     A.sub.6                                      26      232.39912  18.600000                                                  27      -608.94218 19.000000     A.sub.5                                      28      -398.90704 14.911131                                                  29      -141.19742 17.000000     A.sub.4                                      30      -367.14810 0.200000                                                   31      255.48240  27.000000     A.sub.3                                      32      287.16506  152.548704                                                 33      -2807.83665                                                                              33.000000     A.sub.2                                      34      -310.64095 0.097200                                                   35      419.30758  29.000000     A.sub.1                                      36      -1788.71639                                                                              303.707152                                                 *37     -20585.21661                                                                             32.000000     B.sub.1                                                                             L.sub.5                                38      -292.08517 141.774594                                                 39      -331.57665 21.000000     B.sub.2                                                                             L.sub.6                                40      380.00000  6.239286                                                   41      615.03205  45.000000     B.sub.3                                      42      -350.96686 195.254624                                                 43      -860.60392 24.000000     B.sub.4                                      44      277.65121  2.310597                                                   45      304.34780  56.000000     B.sub.5                                                                             L.sub.7                                46      -515.18847 46.552459                                                  47      --         18.195879     AS                                           48      226.73175  25.000000     B.sub.6                                                                             L.sub.8                                *49     231.03852  11.577787                                                  50      282.73561  40.000000     B.sub.7                                      51      -1674.49168                                                                              4.412329                                                   52      169.98274  48.000000     B.sub.8                                      53      1665.64536 63.416012                                                  54      124.88297  33.000000     B.sub.9                                      55      711.33878  8.237993                                                   56      2405.86425 12.000000     B.sub.10                                     57      164.17050  0.100000                                                   58      117.66988  45.000000     B.sub.11                                                                            L.sub.9                                59      1593.84226 6.000000                                                   60      ∞                  W                                            ______________________________________                                    

                  TABLE 5B                                                        ______________________________________                                        ASPHERICAL SURFACE DATA                                                       ______________________________________                                        S37  A =     -0.888458 × 10.sup.-8                                                                 B =     0.557250 × 10.sup.-14                     C =     -0.314040 × 10.sup.-18                                                                D =   -0.462916 × 10.sup.-22                 S49  A =       0.168833 × 10.sup.-7                                                                B =     0.172714 × 10.sup.-12                     C =       0.225018 × 10.sup.-17                                                               D =     0.368469 × 10.sup.-22                ______________________________________                                    

With reference now to FIG. 18 and optical system 180 of Working Example6, light beam seperated mirror M is arranged after reticle R. Inaddition, first imaging optical system A comprises a round-trip opticalsystem wherein, in order from the light beam separating mirror M side,two positive lenses A₁ and A₂, a meniscus lens A₃, a negative meniscuslens A₄, a positive lens A₅, a negative lens A₆, a positive lens A₇, anegative lens A₈, a positive lens A₉, a negative meniscus lens A₁₀ whoseconcave surface faces the light beam separating mirror M side, andconcave mirror M_(C) are arranged.

Second imaging optical system B comprises, in order from the mirror Mside, a positive lens B₁, a negative lens B₂, a positive lens B₃, anegative lens B₄, a positive lens B₅, an aperture stop AS, a meniscuslens B₆, three positive lenses B₇, B₈ and B₉, a negative lens B₁₀, and apositive lens B whose convex surface faces the light beam separatingmirror M side.

                  TABLE 6A                                                        ______________________________________                                        DESIGN SPECIFICATION                                                          ______________________________________                                        Principal Specifications:                                                                     = 193 nm                                                                     (ArF Excimer Laser)                                            β = 1/4   NA = 0.8                                                       H = 70.36 mm   D = 176.0 mm   D.sub.2  = 20.0 mm                              L = 1731 mm    .O slashed..sub.max  = 246 mm                                  Exposure Field: 25 × 6.6 mm                                             |D/H| = 2.50                                                               |D.sub.2 /H| = 0.28                                                        |L/H| = 24.6                  ______________________________________                                        S        r         d             E                                            ______________________________________                                        0        ∞   176.024677    R                                            1        ∞   -20.000000    M                                            2        -1788.71639                                                                             -33.000000    A.sub.1                                                                             L.sub.4                                3        419.30758 -0.097200                                                  4        -268.74569                                                                              -40.000000    A.sub.2                                                                             L.sub.4                                5        -3732.51475                                                                             -132.767922                                                6        239.37693 -27.000000    A.sub.3                                      7        244.82836 -0.216094                                                  8        -2548.31604                                                                             -25.000000    A.sub.4                                      9        -143.32698                                                                              -8.449526                                                  10       -204.90390                                                                              -45.000000    A.sub.5                                      11       -272.57153                                                                              -0.100000                                                  12       327.21563 -17.000000    A.sub.6                                      13       -181.11096                                                                              -5.571460                                                  14       -266.20425                                                                              -25.000000    A.sub.7                                      15       -1015.69653                                                                             -18.600000                                                 16       194.20523 -17.000000    A.sub.8                                                                             L.sub.3                                17       997.00876 -6.595016                                                  18       -338.50796                                                                              -25.000000    A.sub.9                                                                             L.sub.2                                19       -3625.68572                                                                             -29.822032                                                 20       222.83295 -18.000000    A.sub.10                                                                            L.sub.1                                21       455.81520 -42.796334                                                 22       295.50430 42.796334     M.sub.C                                      23       455.81520 18.000000     A.sub.10                                     24       222.83295 29.822032                                                  25       -3625.68572                                                                             25.000000     A.sub.9                                      26       -338.50796                                                                              6.595016                                                   27       997.00876 17.000000     A.sub.8                                      28       194.20523 18.600000                                                  29       -1015.69652                                                                             25.000000     A.sub.7                                      30       -266.20425                                                                              5.571460                                                   31       -181.11096                                                                              17.000000     A.sub.6                                      32       327.21563 0.100000                                                   33       272.57153 45.000000     A.sub.5                                      34       -204.90390                                                                              8.449526                                                   35       -143.32698                                                                              25.000000     A.sub.4                                      36       -2458.31604                                                                             0.216094                                                   37       244.82836 27.000000     A.sub.3                                      38       239.37693 132.767922                                                 39       -3732.51475                                                                             40.000000     A.sub.2                                      40       -268.74569                                                                              0.097200                                                   41       419.30758 33.000000     A.sub.1                                      42       -1788.71639                                                                             322.860627                                                 *43      1988.13960                                                                              40.000000     B.sub.1                                                                             L.sub.5                                44       -346.17707                                                                              118.096619                                                 45       -314.01518                                                                              21.000000     B.sub.2                                                                             L.sub.6                                46       380.00000 7.483728                                                   47       692.44628 45.000000     B.sub.3                                      48       -337.77571                                                                              215.989100                                                 49       -792.05453                                                                              24.000000     B.sub.4                                      50       285.31369 2.593128                                                   51       316.36067 56.000000     B.sub.5                                                                             L.sub.7                                52       -463.77046                                                                              38.289875                                                  53       --        11.964033     AS                                           54       233.30662 25.000000     B.sub.6                                                                             L.sub.8                                *55      234.22897 13.010023                                                  56       255.52550 45.000000     B.sub.7                                      57       -2621.18382                                                                             12.423981                                                  58       181.15092 55.000000     B.sub.8                                      59       3385.66441                                                                              57.958719                                                  60       120.24350 33.000000     B.sub.9                                      61       683.24154 5.786488                                                   62       1209.78340                                                                              12.000000     B.sub.10                                     63       174.98798 0.101872                                                   64       125.78514 45.000000     B.sub.11                                                                            L.sub.9                                65       1885.85548                                                                              6.000000                                                   66       ∞                 W                                            ______________________________________                                    

                  TABLE 6B                                                        ______________________________________                                        ASPLIERICAL SURFACE DATA                                                      ______________________________________                                        S43     A = -0.619385 × 10.sup.-8                                                               B = 0.120817 × 10.sup.-13                               C = -0.197420 × 10.sup.-18                                                              D = -0.295727 × 10.sup.-22                      S55     A = 0.174263 × 10.sup.-7                                                                B = 0.204171 × 10.sup.-12                               C = 0.268111 × 10.sup.-17                                                               D = 0.477853 × 10.sup.-22                       ______________________________________                                    

As can from the aberration plots in FIGS. 15, 17 and 19 correspondingrespectively to Working Examples 4, 5 and 6, excellent imagingperformance at the unit wavelength of 193 nm is obtained and aberrationsare correct to a nearly aberration-free state for each Working Example.

Although reflective surface M is used in Working Example 1 and WorkingExample 3 to seperate light beam b2 that proceeds to concave mirrorM_(C) and light beam b3 reflected from concave mirror M_(C), reflectivesurface M may also be constructed as an apertured reflective mirrorthrough which just reflected light beam b3 from concave mirror M_(C)passes.

In addition, reflective surface M may also be constructed by combining apolarizing beam splitter and 1/4 wavelength plate (not shown) so thatthe polarized light from reticle R is reflected and the polarized lightfrom concave mirror M_(C) passes through.

In the present invention as described above, an optical system thatconstitutes the imaging portion is arranged along a single optical axis,and the reflective surface for separating the light beams is arrangedoutside of the imaging optical system. Consequently, the entire opticalsystem can be examined at the center of the optical axis, and the tiltand shift of each internal lens can be detected.

In other words, adjustment of the optical system is extremely difficultif the bending of the optical axis is performed inside an imagingoptical system, However, in the present invention, adjustment of theoptical system is extremely easy since the reflective surface that bendsthe optical path is arranged outside of the imaging optical systems Aand B.

In addition, when the present invention is applied to a scanning-typeexposure apparatus, the scanning direction of both the reticle and thewafer is the horizontal direction. Accordingly, it is unnecessary tocompensate for the effects of gravity, and scanning is easy to control.

While the present invention has been described in connection withpreferred embodiments and Working Examples, it will be understood thatit is not so limited. On the contrary, it is intended to cover allalternatives, modifications and equivalents as may be included withinthe spirit and scope of the invention as defined in the appended claims.

What is claimed is:
 1. A catadioptric optical system capable of formingan image of an object, comprising:a) a first optical axis having a firstend and a second end, with a concave mirror arranged at said first end,and a second surface orthogonal to said first optical axis at saidsecond end; b) a reflective surface arranged between said concave mirrorand said second surface; c) a first imaging optical system comprising afirst plurality of lenses arranged between said reflective surface andsaid concave mirror; d) a second imaging optical system comprising asecond plurality of lenses arranged between said reflective surface andsaid second surface; e) a second optical axis intersecting said firstoptical axis at said reflective surface and having a first surfacedisposed along and orthogonal to said second optical axis and removedfrom said reflective surface, said first surface being divided intofirst and second regions by a line of intersection between said firstsurface and a plane containing said first optical axis and said secondoptical axis; f) wherein the object is arranged in one of said first andsecond regions of said first surface or first and second regions of saidsecond surface, and the image is formed in one of said first and secondregions of the opposite one of said first or said second surface, saidfirst and second regions of said second surface being formed by dividingsaid second surface by a line of intersection between said secondsurface and the plane containing said first optical axis and said secondoptical axis; and g) wherein an intermediate image of the object isformed in the vicinity of said reflective surface.
 2. A catadioptricoptical system according to claim 1, satisfying the followingconditions:

    0.8<|D.sub.1 /H|<3

    20<|L/H|<30

wherein H is a maximum height of the object as measured from said secondoptical axis, D₁ is a distance along said secondary optical axis fromsaid first surface to the reflective surface, and L is the distancealong said first optical axis from said concave mirror to said secondsurface.
 3. A catadioptric optical system according to claim 2,satisfying the following condition:

    |D.sub.2 /H|<2.5

wherein D₂ is a distance along said first optical axis toward saidconcave mirror from said reflective surface to a lens surface closest tosaid reflective surface.
 4. A catadioptric optical system according toclaim 2, wherein said first imaging optical system includes, in orderalong said first optical axis from said concave mirror side, at least anegative meniscus lens and a positive lens.
 5. A catadioptric opticalsystem according to claim 4, wherein said first optical imaging systemfurther includes, in order along said first optical axis from saidconcave mirror side, at least a positive lens L₂ and a negative lens L₃between said negative meniscus lens L₁ and positive lens L₄.
 6. Acatadioptric optical system according to claim 1, satisfying thefollowing condition:

    |D.sub.2 /H|<2.5

wherein D₂ is a distance along said first optical axis toward saidconcave mirror from said reflective surface to a lens surface closest tosaid reflective surface, and H is a maximum height of the object asmeasured from said second optical axis.
 7. A catadioptric optical systemaccording to claim 1, wherein said first imaging optical systemincludes, in order along said first optical axis from said concavemirror side, at least a negative meniscus lens and a positive lens.
 8. Acatadioptric optical system according to claim 7, wherein said firstoptical imaging system further includes, in order along said firstoptical axis from said concave mirror side, at least a positive lens L₂and a negative lens L₃ between said negative meniscus lens L₁ andpositive lens L₄.
 9. A catadioptric optical system according to claim 7,wherein said second imaging optical system includes an aperture stop, atleast a positive lens L₇ in the vicinity of said aperture stop, and atleast a positive lens L₉ whose convex surface faces said reflectivesurface and which is immediately adjacent said second surface.
 10. Acatadioptric optical system according to claim 1, wherein said secondimaging optical system includes an aperture stop, at least a positivelens L₇ in the vicinity of said aperture stop, and at least a positivelens L₉ whose convex surface faces said reflective surface and which isimmediately adjacent said second surface.
 11. A catadioptric opticalsystem according to claim 10, wherein said second imaging optical systemincludes at least a positive lens L₅ after said reflective surface, atleast a positive lens L₇ and a meniscus lens L₈ provided in the vicinityof said aperture stop, and at least a positive lens L₉ whose convexsurface faces said reflective surface is provided immediately adjacentsaid second surface.
 12. A catadioptric optical system according toclaim 1, including at least two or more aspherical lens surfaces.
 13. Acatadioptric optical system according to claim 1, wherein said lenses insaid first and second plurality of lenses are formed of the same glassmaterial.